If I understand the OP correctly, he lives in Belgium, works for an Irish Airline and is, presumably, paid in Euros. So far so good.
Because his pay originates in Ireland, it's subject to the social welfare deduction. (What I used to pay as National Insurance Contributions when I lived in Blighty). Again, so far, so good.
But, he gets sick and, because he doesn't live in Ireland, he can't claim pay-outs from the social welfare fund, which he's paid into for six years. It's even possible that, because he hasn't contributed to the Belgian equivalent (if there is one), for six years, he can't claim (full) benefits from the Belgian fund.
Does no one else see an element of unfairness here?
I don't think RYR can take the blame here, but the Irish Government could be possibly accused of greed - and of demanding money under false pretences?